1. Field of the Invention
This invention relates generally to a method for computing mean effective pressure in an engine and, more particularly, to a method for computing indicated mean effective pressure (IMEP) in an internal combustion engine using a cubic spline integration method which provides a highly accurate result even when using a low-resolution crankshaft position encoder and using less frequent measurement of cylinder pressure input data than required by existing IMEP calculation methods.
2. Discussion of the Related Art
Most modern internal combustion engines employ a number of sophisticated control strategies to optimize performance, fuel economy, emissions, and other factors. Among the many parameters used to control an engine's operation, indicated mean effective pressure (IMEP) is one of the more important. IMEP is used as a measure of the amount of work an engine is performing, or as a measure of the torque that is being provided by the engine. Engine control strategies are often designed around IMEP, and of course these strategies will be effective for controlling the engine only if IMEP is calculated with a sufficient degree of accuracy.
While methods for calculation of IMEP are known in the art, existing methods require a high-resolution crankshaft position encoder and frequent measurement of cylinder pressure data in order to obtain an accurate IMEP calculation. Requiring high-resolution crankshaft position and cylinder pressure data has a number of disadvantages, including the cost of the crank position encoder, the cost associated with the digital memory required to store the high-resolution cylinder pressure data over time, and the cost associated with computing power needed in electronic control units in order to process the large amounts of crank position and cylinder pressure data for IMEP calculations.
A need exists for a method of calculating indicated mean effective pressure which provides the accuracy needed for proper control of the engine, but which does not require high-resolution crankshaft position and cylinder pressure data as input. Such a method can provide a significant benefit in terms of cost savings and simplification for a manufacturer of engines or vehicles.